An ELT Glossary : Tag questions / Question tags

A tag question is a question formulated as a statement with the operator and subject (a question tag) following. The sentences below are all examples of tag questions, while the underlined section is the question tag :

He's from London, isn't he?
So you passed, did you?
You haven't seen my slippers, have you?
You can speak French, can't you?
So you don't want it, don't you?

Different combinations of negative/affirmative statements plus negative/affirmative tags, coupled with intonational differences, give different meanings to the sentences.

For a full account see...

Quirk et al,(1972)   A Grammar of Contemporary English, Longman Sections 7.59-60

And for some teaching suggestions...

Scrivener, J. Teaching English Grammar, Macmillan